1. Technical Field of the Invention
This invention relates to a double nut for use in fastening two nuts against a bolt in order to fix various kinds of machine devices or iron frames of a building or the like. This invention relates to an outside lock nut which is overlapped on a fastening nut so as to fasten the nut to prevent the fastening nut from being loosened.
2. Description of the Prior Art
A bolt and a nut for use in fastening component parts to various kinds of machine devices in the prior art or a bolt and a nut used in the case of fixing an iron frame of a building or the like are gradually loosened by vibration of the machine devices or the like. In view of this fact, there have been proposed various kinds of means for preventing looseness of such a nut as above.
For example, as shown in FIGS. 10(a), (b), there is provided means in which "a spring washer" is used. This spring washer 51 is made such that a part of the washer having a resilient force is cut and each of the cut portions 51a, 51a is slightly bent to their opposite directions. This spring washer 51 is inserted onto the bolt 52, placed between a seat surface 53a of the nut 53 and a fastening surface of the machine device or the like so as to generate always a tension force between the seat surface 53a of the nut 53 and the fastening surface and then the nut 53 is prevented from being loosened. In addition, in place of this spring washer 51, it is also possible to apply a toothed washer (not shown). This toothed washer is used for preventing the nut from being loosened by biting the teeth into the fastening surface with the fastening force of the nut.
In addition, as shown in FIGS. 11(a), (b), it is also possible to apply means in which a "pin" is passed through the nut. Means for passing the pin through this nut is made such that common through-pass holes 64, 65 are arranged in the threaded part 62 of the bolt 61 and the nut 63, a pin 66 such as a cotter pin, a tapered pin or the like is inserted into these through-pass holes 64, 65 so as to prevent positively the nut 63 from being loosened. In this case, in place of the through-pass hole 65 of this nut 63, there is proposed means in which a seat surface of the nut 63 is provided with a plurality of grooves in a radial manner, pins are engaged with these grooves to prevent the nut from being rotated and to prevent looseness of the nut.
Further, as shown in FIG. 12(a), as a simple looseness preventive means which is frequently used in the prior art, there is provided a double-nut. This double nut is operated such that another looseness preventive nut 71b is overlapped on a fastening nut 71a against a bolt 72 and only the outer nut 71b is further fastened forcedly. This double nut is applied in order to prevent these nuts 71a, 71b from being loosened due to vibration of the machine device or the like under fastening action of these nuts 71a, 71b (refer to FIG. 12(b)).
It can be expected that the aforesaid prior art spring washer 51 may provide an effect of preventing looseness just after its fastening. However, its use of longer period causes a resilient force of the spring washer 51 to be decreased and an effect of preventing looseness to be reduced. In addition, this prior art nut had a problem that the nut is not suitable for fastening of a heavy iron frame such as a building or the like. Similarly, although it could be expected that the toothed washer may provide an effect of preventing looseness against material quality such as a soft wooden product as compared with that of a metallic product of a small-sized machine device or a fastening component element, it could not be expected that an effect of preventing looseness is attained for a large-sized metallic machine device or the like.
In addition, means in which the pin 66 is passed through the nut 63 is made such that there are provided through-pass holes 64, 65 common to the threaded part 62 of the bolt 61 and the nut 63. Accordingly, when another nut is fastened, a position of each of the through-pass holes 64, 65 is not coincided to each other and the pin may not be passed through the through-pass holes. Further, even if the same nut 63 was applied, a position of each of the through-pass holes 64, 65 was not coincided to each other when the nut was fastened against the bolt 61. In turn, when the nut 63 was fastened against the bolt 61 in such a way that the positions of each of the through-pass holes 64, 65 are coincided to each other, it showed a problem that they are fastened in loosened state, resulting in that they can not be forcedly fastened.
In addition, when the double nut was fastened at one location, it was necessary to fasten nuts 71a, 71b twice and an operating step for further fastening only the outer nut 71b was added, resulting in that a quite troublesome fastening step was attained. In particular, the machine device or building requiring a large amount of nut fastening operations had a problem that the fastening steps might become a cause to delay a completion of work. In addition, since the work for confirming it individually whether or not the looseness preventive outer nut 71b is forcedly fastened was troublesome, it showed a problem that the twice fastening of the nut is easily forgotten.
The present invention has been invented in view of the aforesaid problems and it is an object of the present invention to provide a lock nut in which a seat surface of the looseness-preventive nut in the double nut is formed with a plurality of projections, thereby when the nut is fastened against the bolt, these projections are deformed and collapsed to increase a frictional force caused by biting of the projections into the threaded part of the bolt.